Some conventional projection type vehicle lighting units have been proposed which utilize a light guide body configured to guide light from a light source to an emission surface so that the light can exit through the emission surface for illumination. For example, such vehicle lighting units have been disclosed in Japanese Patent Application Laid-Open No. 2010-108639 (or JP5196314B).
FIG. 1 is a perspective view illustrating a vehicle lighting unit 200 described in Japanese Patent Application Laid-Open No. 2010-108639.
As illustrated in FIG. 1, the vehicle lighting unit 200 described in Japanese Patent Application Laid-Open No. 2010-108639 is a projection type vehicle lighting unit that can include a light source 210 and a light guiding body 220. The light guiding body 220 can be configured by a transparent member, and include: a light incident surface 220a of a semispheric recess; a reflection surface 220b configured to reflect light entering the light guiding body 220 through the light incident surface 220a; a light exiting surface 220c configured to cause the light gathered by the reflection surface 220b to exit therethrough; an edge portion 220d; and a flat surface 220e extending from the edge portion 220d and configured to function as a reflection surface. A region of the flat surface 220e at or near the edge portion 220d is subjected to an anti-reflection treatment, wherein the region corresponds to the region A1 between the lines L1 and L3 and the region A2 between the lines L2 and L4 in FIG. 1.
In the vehicle lighting unit 200 with the above configuration, when the spherical aberration is removed from the light exiting surface 220c, the curvature of the light exiting surface 220c is decreased. As a result, as illustrated in FIG. 2A, part of light being guided through the light guiding body 220 can be internally reflected by the light exiting surface 220c to cause loss of light amount. Further, the light that is internally reflected is originally allowed to exit through the light exiting surface 220c to be horizontally diffused for the illumination of right and left portions of the given light distribution pattern. However, as a result of the above internal reflection of light, the illuminance at the right and left portions of the light distribution pattern is disadvantageously decreased.
According to the sign conditions (conditions for removing comma aberration), the improvement of comma aberration requires the principal surface of the light exiting surface 220c near the light source 210 to coincide with (or substantially coincide with) a sphere of which center is located at the rear side focal point F220c of the light exiting surface 220c (so-called, Apollo's circle). However, in the vehicle lighting device 200 with the above configuration, as illustrated in FIG. 2B, even when the spherical aberration is removed, the principal surface of the light exiting surface 220c near the light source 210, or the light exiting surface 220c itself, is largely deviated from the sphere of which center is located at the rear side focal point F220c of the light exiting surface 220c (so-called, Apollo's circle), whereby the comma aberration cannot be improved. As a result, the vehicle lighting unit 200 with the above configuration can generate glare light due to the comma aberration formed above the horizontal line H in the light distribution pattern as illustrated in FIG. 3, meaning that a clear cut-off line cannot be formed.
In order to prevent glare light from being generated above the horizontal line H in the vehicle lighting unit 200 with the above configuration, the region of the flat surface 220e near the edge portion 220d (the region corresponds to the region A1 between the lines L1 and L3 and the region A2 between the lines L2 and L4 in FIG. 1) must be subjected to an anti-reflection treatment, resulting in lowering the light utilization efficiency.